The concept of coating glass containers and the like in order to make them stronger and shatter-resistant is not new but is an idea which has received considerable attention lately because of increased safety standards demanded by the public and required by governments of glass bottle manufacturers.
The bottles or other containers are basically a glass vessel covered or coated with the plastic material. The coated containers are substantially lighter than an all glass container because the walls of the container can be thinner than conventional. As much as a third (1/3) less glass than conventional is employed.
The coated glass containers have numerous advantages over the all glass containers. They are shatter-resistant, lightweight and have the ability to run on standard bottling and handling equipment. Additionally, the plastic surface can be directly printed on thereby eliminating the application of a label. It has been reported that the coated bottles withstood an average of 80 tipovers without shattering while conventional glass containers withstood an average of 4tipovers. Further, the coated containers can be packed in corrugated containers without partitions and will resist breakage as well as standard glass containers packed with partitions. The light weight of the bottles also reduces shipping and handling costs. A still further advantage is that the coating, while permitting the bottles to run on conventional processing lines, reduces noise on the equipment. In addition, less breakage occurs during the filling operation which reduces overall cost and improves safety.
One type of plastic coating which has been suggested for this type of application is a nylon coating which imparts a smooth, clear finish to the glass when it is sprayed on. A second type, now in commercial use, uses an ethylene copolymer "skin" that envelops the glass bottle from neck to base (see e.g., U.S. Pat. No. 3,415,673). This copolymer coating has a rough finish that imparts a frosty appearance to the container. Another type of coating currently commercially available is based on an epoxy copolymer which is primarily designed to shield the contents of the bottle from ultraviolet light.
Another type of plastic currently commercially available is a foamed polystyrene label which is heat-shrunk onto the glass container. The foamed polystyrene has the advantages of being lightweight and has good shrinkage properties but is relatively expensive and its tensile strength properties are relatively poor.
It is therefore the object of this invention to provide a new lightweight, strong, uniform plastic coating which can be heat-shrunk onto a tubular substrate such as a glass bottle rapidly and uniformly, presenting a product with good opacity, which retains all of the advantages of the prior art materials and eliminates the deficiencies thereof. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.